Hydrogen sulphide occurs in various gas streams, for example, in sour natural gas streams and in tail gas streams from various industrial operations in which sulphur containing fuels and combustible materials are burned. Hydrogen sulphide is a highly toxic and odiferous substance, which must be substantially removed from gas streams before their ultimate discharge to atmosphere.
Various processes have been proposed which generally involve the conversion of the hydrogen sulphide to sulphur. One prior art process is that described in U.S. Pat. No. 2,899,267 (Berndt et al), wherein the purification of a hydrogen sulphide-containing air stream is effected by passing the gas stream through an alkaline iron hydroxide suspension. The process is described in this reference as a two-step process, involving an initial formation of ferrous sulfide for the hydrogen sulfide and subsequent oxidation of the ferric sulfide to sulfur.
In another prior art process, described in U.S. Pat. No. 3,068,065, the hydrogen sulphide-containing stream is contacted with a solution of ferric iron complexed with ethylene diamine tetraacetic acid. In this reference, the hydrogen sulphide is similarly removed by reaction to form ferrous sulphide. The solution then is reoxidized in a separate operation to form the ferric ion and sulphur. The sulphur formed in these prior art procedures is separated in an additional processing step.
U.S. Pat. No. 4,099,251 (Meuly) describes a method for removing sulfur dioxide from gaseous streams by oxidation in the presence of a polyvalent chelate solution. Again, a two-step process is described in which ferric iron reacts with the hydrogen sulfide in a first step and the depleted ferric iron is regenerated by oxidation to form sulfur. While this reference describes a variety of specific gas/liquid contacting systems for effecting the reactions, this reference does not describe the specific equipment used in the present invention.
U.S. Pat. No. 4,315,903 (Fenton et al) describes a two-stage operation for contacting a hydrogen sulfide-containing gas stream with an aqueous solution of a specific type of catalyst, namely a water-soluble metal vanadate and water-soluble anthraquinone disulfonate, in a first vessel followed by oxidative regeneration of the spent contact solution with formation of sulfur.
U.S. Pat. No. 4,189,462 (Thompson) is similar to the Fenton patent described above in describing a two-stage sulfur removal by contact of the hydrogen sulfide stream with a reagent and reagent regeneration using oxygen, but differs in that the reactions are carried out in separate zones of a single reaction vessel. The sulfur is removed from the oxidative regeneration zone as a slurry and is removed by filtration.
U.S. Pat. No. 3,933,992 (Andral) describes a procedure for automated regulation of sulfur production units which produce sulfur by the Claus reaction, by regulating the flow of oxygen based on measurement of the concentration of sulfur compounds in a product gas stream.
U.S. Pat. No. 4,036,942 (Sibeud) describes the removal of hydrogen sulfide from gaseous product streams by reaction with oxygen in the presence of a metal amino acid chelate. The processes described require long contact times.